Fe(III) (oxyhydr)oxide reduction by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens

Some thermophilic bacteria from deep-sea hydrothermal vents grow by dissimilatory iron reduction, but our understanding of their biogenic mineral transformations is nascent. Mineral transformations catalyzed by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens during growth at 55°C were examined using synthetic nanophase ferrihydrite, akaganeite, and lepidocrocite separately as terminal electron acceptors. Spectral analyses using visible-near infrared (VNIR), Fourier-transform infrared attenuated total reflectance (FTIR-ATR), and Mössbauer spectroscopies were complemented with x-ray diffraction (XRD) and transmission electron microscopy (TEM) using selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analyses. The most extensive biogenic mineral transformation occurred with ferrihydrite, which produced a magnetic, visibly dark mineral with spectral features matching cation-deficient magnetite. Desulfovulcanus ferrireducens also grew on akaganeite and lepidocrocite and produced non-magnetic, visibly dark minerals that were poorly soluble in the oxalate solution. Bioreduced mineral products from akaganeite and lepidocrocite reduction were almost entirely absorbed in the VNIR spectroscopy in contrast to both parent minerals and the abiotic controls. However, FTIR-ATR and Mössbauer spectra and XRD analyses of both biogenic minerals were almost identical to the parent and control minerals. The TEM of these biogenic minerals showed the presence of poorly crystalline iron nanospheres (50-200 nm in diameter) of unknown mineralogy that were likely coating the larger parent minerals and were absent from the controls. The study demonstrated that thermophilic bacteria transform different types of Fe(III) (oxyhydr)oxide minerals for growth with varying mineral products. These mineral products are likely formed through dissolution-reprecipitation reactions but are not easily predictable through chemical equilibrium reactions alone.

Spectral Detection of Nanophase Iron Minerals Produced by Fe(III)-Reducing Hyperthermophilic Crenarchaea

Mineral transformations by two hyperthermophilic Fe(III)-reducing crenarchaea, Pyrodictium delaneyi and Pyrobaculum islandicum, were examined using synthetic nanophase ferrihydrite, lepidocrocite, and akaganeite separately as terminal electron acceptors and compared with abiotic mineral transformations under similar conditions. Spectral analyses using visible-near-infrared, Fourier-transform infrared attenuated total reflectance (FTIR-ATR), Raman, and Mössbauer spectroscopies were complementary and revealed formation of various biomineral assemblages distinguishable from abiotic phases. The most extensive biogenic mineral transformation occurred with ferrihydrite, which formed primarily magnetite with spectral features similar to biomagnetite relative to a synthetic magnetite standard. The FTIR-ATR spectra of ferrihydrite bioreduced by P. delaneyi also showed possible cell-associated organics such as exopolysaccharides. Such combined detections of biomineral assemblages and organics might serve as biomarkers for hyperthermophilic Fe(III) reduction. With lepidocrocite, P. delaneyi produced primarily a ferrous carbonate phase reminiscent of siderite, and with akaganeite, magnetite and a ferrous phosphate phase similar to vivianite were formed. P. islandicum showed minor biogenic production of a ferrous phosphate similar to vivianite when grown on lepidocrocite, and a mixed valent phosphate or sulfate mineral when grown on akaganeite. These results expand the range of biogenic mineral transformations at high temperatures and identify spacecraft-relevant spectroscopies suitable for discriminating mineral biogenicity.

Formate and hydrogen in hydrothermal vents and their use by extremely thermophilic methanogens and heterotrophs

Extremely thermophilic methanogens in the Methanococci and heterotrophs in the Thermococci are common in deep-sea hydrothermal vents. All Methanococci use H₂ as an electron donor, and a few species can also use formate. Most Methanococci have a coenzyme F₄₂₀-reducing formate dehydrogenase. All Thermococci reduce S⁰ but have hydrogenases and produce H₂ in the absence of S⁰. Some Thermococci have formate hydrogenlyase (Fhl) that reversibly converts H₂ and CO₂ to formate or an NAD(P)⁺-reducing formate dehydrogenase (Nfd). Questions remain if Methanococci or Thermococci use or produce formate in nature, why only certain species can grow on or produce formate, and what the physiological role of formate is? Formate forms abiotically in hydrothermal fluids through chemical equilibrium with primarily H₂, CO₂, and CO and is strongly dependent upon H₂ concentration, pH, and temperature. Formate concentrations are highest in hydrothermal fluids where H₂ concentrations are also high, such as in ultramafic systems where serpentinization reactions occur. In nature, Methanococci are likely to use formate as an electron donor when H₂ is limiting. Thermococci with Fhl likely convert H₂ and CO₂ to formate when H₂ concentrations become inhibitory for growth. They are unlikely to grow on formate in nature unless formate is more abundant than H₂ in the environment. Nearly all Methanococci and Thermococci have a gene for at least one formate dehydrogenase catalytic subunit, which may be used to provide free formate for de novo purine biosynthesis. However, only species with a membrane-bound formate transporter can grow on or secrete formate. Interspecies H₂ transfer occurs between Thermococci and Methanococci. This and putative interspecies formate transfer may support Methanococci in low H₂ environments, which in turn may prevent growth inhibition of Thermococci by its own H₂. Future research directions include understanding when, where, and how formate is used and produced by these organisms in nature, and how transcription of Thermococci genes encoding formate-related enzymes are regulated.

Acceptor dependent catalytic properties of GH57 4-α-glucanotransferase from Pyrococcus sp. ST04

The 4-α-glucanotransferase (4-α-GTase or amylomaltase) is an essential enzyme in maltodextrin metabolism. Generally, most bacterial 4-α-GTase is classified into glycoside hydrolase (GH) family 77. However, hyperthermophiles have unique 4-α-GTases belonging to GH family 57. These enzymes are the main amylolytic protein in hyperthermophiles, but their mode of action in maltooligosaccharide utilization is poorly understood. In the present study, we investigated the catalytic properties of 4-α-GTase from the hyperthermophile Pyrococcus sp. ST04 (PSGT) in the presence of maltooligosaccharides of various lengths. Unlike 4-α-GTases in GH family 77, GH family 57 PSGT produced maltotriose in the early stage of reaction and preferred maltose and maltotriose over glucose as the acceptor. The kinetic analysis showed that maltotriose had the lowest KM value, which increased amylose degradation activity by 18.3-fold. Structural models of PSGT based on molecular dynamic simulation revealed two aromatic amino acids interacting with the substrate at the +2 and +3 binding sites, and the mutational study demonstrated they play a critical role in maltotriose binding. These results clarify the mode of action in carbohydrate utilization and explain acceptor binding mechanism of GH57 family 4-α-GTases in hyperthermophilic archaea.

Desulfovulcanus ferrireducens gen. nov., sp. nov., a thermophilic autotrophic iron and sulfate-reducing bacterium from subseafloor basalt that grows on akaganéite and lepidocrocite minerals

A deep-sea thermophilic bacterium, strain Ax17^T, was isolated from 25 °C hydrothermal fluid at Axial Seamount. It was obligately anaerobic and autotrophic, oxidized molecular hydrogen and formate, and reduced synthetic nanophase Fe(III) (oxyhydr)oxide minerals, sulfate, sulfite, thiosulfate, and elemental sulfur for growth. It produced up to 20 mM Fe²⁺ when grown on ferrihydrite but < 5 mM Fe²⁺ when grown on akaganéite, lepidocrocite, hematite, and goethite. It was a straight to curved rod that grew at temperatures ranging from 35 to 70 °C (optimum 65 °C) and a minimum doubling time of 7.1 h, in the presence of 1.5–6% NaCl (optimum 3%) and pH 5–9 (optimum 8.0). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain was 90–92% identical to other genera of the family Desulfonauticaceae in the phylum Pseudomonadota. The genome of Ax17^T was sequenced, which yielded 2,585,834 bp and contained 2407 protein-coding sequences. Based on overall genome relatedness index analyses and its unique phenotypic characteristics, strain Ax17^T is suggested to represent a novel genus and species, for which the name Desulfovulcanus ferrireducens is proposed. The type strain is Ax17^T (= DSM 111878^T = ATCC TSD-233^T).

Determination of Polydextrose as Dietary Fiber in Foods

Polydextrose (Litesse®) provides physiological effects consistent with dietary fiber. However, AOAC methods for measuring total dietary fiber (TDF) in foods include an ethanol precipitation step in which polydextrose and similar carbohydrates are discarded and therefore not quantitated. This study describes a method developed to quantitate polydextrose in foods. The new method includes water extraction, centrifugal ultrafiltration, multienzyme hydrolysis, and anion exchange chromatography with electrochemical detection. Six foods were prepared with 4 levels of polydextrose to test the ruggedness of the method. Internal validation demonstrated the ruggedness of the method with recoveries ranging from 83 to 104% with an average of 95% (n = 24) and relative standard deviation of recoveries ranging from 0.7 to 13% with an average of 3.3% (n = 24). The value is added to that obtained for dietary fiber content of foods using the AOAC methods, to determine the TDF content of the food.

Fluid geochemistry, local hydrology, and metabolic activity define methanogen community size and composition in deep-sea hydrothermal vents

The size and biogeochemical impact of the subseafloor biosphere in oceanic crust remain largely unknown due to sampling limitations. We used reactive transport modeling to estimate the size of the subseafloor methanogen population, volume of crust occupied, fluid residence time, and nature of the subsurface mixing zone for two low-temperature hydrothermal vents at Axial Seamount. Monod CH4 production kinetics based on chemostat H2 availability and batch-culture Arrhenius growth kinetics for the hyperthermophile Methanocaldococcus jannaschii and thermophile Methanothermococcus thermolithotrophicus were used to develop and parameterize a reactive transport model, which was constrained by field measurements of H2, CH4, and metagenome methanogen concentration estimates in 20-40 °C hydrothermal fluids. Model results showed that hyperthermophilic methanogens dominate in systems where a narrow flow path geometry is maintained, while thermophilic methanogens dominate in systems where the flow geometry expands. At Axial Seamount, the residence time of fluid below the surface was 29-33 h. Only 1011 methanogenic cells occupying 1.8-18 m3 of ocean crust per m2 of vent seafloor area were needed to produce the observed CH4 anomalies. We show that variations in local geology at diffuse vents can create fluid flow paths that are stable over space and time, harboring persistent and distinct microbial communities.

Growth Kinetics, Carbon Isotope Fractionation, and Gene Expression in the Hyperthermophile Methanocaldococcus jannaschii during Hydrogen-Limited Growth and Interspecies Hydrogen Transfer

Hyperthermophilic methanogens are often H2 limited in hot subseafloor environments, and their survival may be due in part to physiological adaptations to low H2 conditions and interspecies H2 transfer. The hyperthermophilic methanogen Methanocaldococcus jannaschii was grown in monoculture at high (80 to 83 μM) and low (15 to 27 μM) aqueous H2 concentrations and in coculture with the hyperthermophilic H2 producer Thermococcus paralvinellae The purpose was to measure changes in growth and CH4 production kinetics, CH4 fractionation, and gene expression in M. jannaschii with changes in H2 flux. Growth and cell-specific CH4 production rates of M. jannaschii decreased with decreasing H2 availability and decreased further in coculture. However, cell yield (cells produced per mole of CH4 produced) increased 6-fold when M. jannaschii was grown in coculture rather than monoculture. Relative to high H2 concentrations, isotopic fractionation of CO2 to CH4 (εCO2-CH4) was 16‰ larger for cultures grown at low H2 concentrations and 45‰ and 56‰ larger for M. jannaschii growth in coculture on maltose and formate, respectively. Gene expression analyses showed H2-dependent methylene-tetrahydromethanopterin (H4MPT) dehydrogenase expression decreased and coenzyme F420-dependent methylene-H4MPT dehydrogenase expression increased with decreasing H2 availability and in coculture growth. In coculture, gene expression decreased for membrane-bound ATP synthase and hydrogenase. The results suggest that H2 availability significantly affects the CH4 and biomass production and CH4 fractionation by hyperthermophilic methanogens in their native habitats.IMPORTANCE Hyperthermophilic methanogens and H2-producing heterotrophs are collocated in high-temperature subseafloor environments, such as petroleum reservoirs, mid-ocean ridge flanks, and hydrothermal vents. Abiotic flux of H2 can be very low in these environments, and there is a gap in our knowledge about the origin of CH4 in these habitats. In the hyperthermophile Methanocaldococcus jannaschii, growth yields increased as H2 flux, growth rates, and CH4 production rates decreased. The same trend was observed increasingly with interspecies H2 transfer between M. jannaschii and the hyperthermophilic H2 producer Thermococcus paralvinellae With decreasing H2 availability, isotopic fractionation of carbon during methanogenesis increased, resulting in isotopically more negative CH4 with a concomitant decrease in H2-dependent methylene-tetrahydromethanopterin dehydrogenase gene expression and increase in F420-dependent methylene-tetrahydromethanopterin dehydrogenase gene expression. The significance of our research is in understanding the nature of hyperthermophilic interspecies H2 transfer and identifying biogeochemical and molecular markers for assessing the physiological state of methanogens and possible source of CH4 in natural environments.

Reduction and Morphological Transformation of Synthetic Nanophase Iron Oxide Minerals by Hyperthermophilic Archaea

Fe(III) (oxyhydr)oxides are electron acceptors for some hyperthermophilic archaea in mildly reducing geothermal environments. However, the kinds of iron oxides that can be used, growth rates, extent of iron reduction, and the morphological changes that occur to minerals are poorly understood. The hyperthermophilic iron-reducing crenarchaea Pyrodictium delaneyi and Pyrobaculum islandicum were grown separately on six different synthetic nanophase Fe(III) (oxyhydr)oxides. For both organisms, growth on ferrihydrite produced the highest growth rates and the largest amounts of Fe(II), although P. delaneyi produced four times more Fe(II) (25 mM) than P. islandicum (6 mM). Both organisms grew on lepidocrocite and akaganéite and produced 2 and 3 mM Fe(II). Modest growth occurred for both organisms on goethite, hematite, and maghemite where ≤1 mM Fe(II) was produced. The diameters of the spherical mineral end-products following P. delaneyi growth increased by 30 nm for ferrihydrite and 50–150 nm for lepidocrocite relative to heated abiotic controls. For akaganéite, spherical particle sizes were the same for P. delaneyi-reacted samples and heated abiotic controls, but the spherical particles were more numerous in the P. delaneyi samples. For P. islandicum, there was no increase in grain size for the mineral end-products following growth on ferrihydrite, lepidocrocite, or akaganéite relative to the heated abiotic controls. High-resolution transmission electron microscopy of lattice fringes and selected-area electron diffraction of the minerals produced by both organisms when grown on ferrihydrite showed that magnetite and/or possibly maghemite were the end-products while the heated abiotic controls only contained ferrihydrite. These results expand the current view of bioavailable Fe(III) (oxyhydr)oxides for reduction by hyperthermophilic archaea when presented as synthetic nanophase minerals. They show that growth and reduction rates are inversely correlated with the iron (oxyhydr)oxide crystallinity and that iron (oxyhydr)oxide mineral transformation takes different forms for these two organisms.

Spectral and morphological characteristics of synthetic nanophase iron (oxyhydr)oxides

Nanophase iron (oxyhydr)oxides are ubiquitous on Earth, globally distributed on Mars, and likely present on numerous other rocky solar system bodies. They are often structurally and, therefore, spectrally distinct from iron (oxyhydr)oxide bulk phases. Because their spectra vary with grain size, they can be difficult to identify or distinguish unless multiple analysis techniques are used in tandem. Yet, most literature reports fail to use multiple techniques or adequately parameterize sample morphology, making it difficult to understand how morphology affects spectral characteristics across techniques. Here, we present transmission electron microscopy, Raman, visible and near-infrared, and mid-infrared attenuated total reflectance data on synthetic, nanophase akaganéite, lepidocrocite, goethite, hematite, ferrihydrite, magnetite, and maghemite. Feature positions are tabulated and compared to those for bulk (oxyhydr)oxides and other nanophase iron (oxyhydr)oxides from the literature. The utility and limitations of each technique in analyzing nanophase iron (oxyhydr)oxides are discussed. Raman, mid-infrared, and visible near-infrared spectra show broadening, loss of some spectral features, and shifted positions compared to bulk phases. Raman and mid-infrared spectroscopies are useful in identifying and distinguishing akaganéite, lepidocrocite, goethite, and hematite, though ferrihydrite, magnetite, and maghemite have overlapped band positions. Visible near-infrared spectroscopy can identify and distinguish among ferrihydrite, magnetite, and maghemite in pure spectra, though akaganéite, lepidocrocite, and goethite can have overlapping bands. It is clear from this work that further understanding of variable spectral features in nanophase iron (oxyhydr)oxides must await additional studies to robustly assess effects of morphology. This study establishes a template for future work.

Biological iron-sulfur storage in a thioferrate-protein nanoparticle

Iron–sulfur clusters are ubiquitous in biology and function in electron transfer and catalysis. They are assembled from iron and cysteine sulfur on protein scaffolds. Iron is typically stored as iron oxyhydroxide, ferrihydrite, encapsulated in 12 nm shells of ferritin, which buffers cellular iron availability. Here we have characterized IssA, a protein that stores iron and sulfur as thioferrate, an inorganic anionic polymer previously unknown in biology. IssA forms nanoparticles reaching 300 nm in diameter and is the largest natural metalloprotein complex known. It is a member of a widely distributed protein family that includes nitrogenase maturation factors, NifB and NifX. IssA nanoparticles are visible by electron microscopy as electron-dense bodies in the cytoplasm. Purified nanoparticles appear to be generated from 20 nm units containing ∼6,400 Fe atoms and ∼170 IssA monomers. In support of roles in both iron–sulfur storage and cluster biosynthesis, IssA reconstitutes the [4Fe-4S] cluster in ferredoxin in vitro.

The biosynthesis of iron-sulfur clusters in anaerobic organisms has not been extensively investigated. Here, the authors identify and characterize a multi-subunit protein that stores iron and sulfur in thioferrate for the assembly of the clusters in Pyrococcus furiosus.

Broad substrate specificity of a hyperthermophilic α-glucosidase from Pyrobaculum arsenaticum

Pyrobaculum arsenaticum is a hyperthermophilic archaeon that thrives at 95°C. This strain encodes a putative GH31 intracellular α-glucosidase (Pars_2044, PyAG) in its genome. The recombinant PyAG (rPyAG) was optimally expressed in Escherichia coli at 37°C for 4 h after IPTG induction. The purified rPyAG is a homotetrameric α-glucosidase that exhibited highly thermostable properties. Maximum p-nitrophenyl-α-D-glucopyranoside (pNPG) hydrolysis activity was observed at 90°C and pH 5.0. The enzyme mainly recognized the non-reducing end of the substrate, releasing the glucose unit. rPyAG also had broad substrate specificity, cleaving maltose (α-1,4-linkage), kojibiose (α-1,2-linkage), and nigerose (α-1,3-linkage) with similar efficiency. Based on these results, rPyAG can be used to modify health-relevant sugar conjugates linked by α-1,2- or α-1,3-bonds.

Hydrogen Limitation and Syntrophic Growth among Natural Assemblages of Thermophilic Methanogens at Deep-sea Hydrothermal Vents

Thermophilic methanogens are common autotrophs at hydrothermal vents, but their growth constraints and dependence on H2 syntrophy in situ are poorly understood. Between 2012 and 2015, methanogens and H2-producing heterotrophs were detected by growth at 80°C and 55°C at most diffuse (7-40°C) hydrothermal vent sites at Axial Seamount. Microcosm incubations of diffuse hydrothermal fluids at 80°C and 55°C demonstrated that growth of thermophilic and hyperthermophilic methanogens is primarily limited by H2 availability. Amendment of microcosms with NH4 (+) generally had no effect on CH4 production. However, annual variations in abundance and CH4 production were observed in relation to the eruption cycle of the seamount. Microcosm incubations of hydrothermal fluids at 80°C and 55°C supplemented with tryptone and no added H2 showed CH4 production indicating the capacity in situ for methanogenic H2 syntrophy. 16S rRNA genes were found in 80°C microcosms from H2-producing archaea and H2-consuming methanogens, but not for any bacteria. In 55°C microcosms, sequences were found from H2-producing bacteria and H2-consuming methanogens and sulfate-reducing bacteria. A co-culture of representative organisms showed that Thermococcus paralvinellae supported the syntrophic growth of Methanocaldococcus bathoardescens at 82°C and Methanothermococcus sp. strain BW11 at 60°C. The results demonstrate that modeling of subseafloor methanogenesis should focus primarily on H2 availability and temperature, and that thermophilic H2 syntrophy can support methanogenesis within natural microbial assemblages and may be an important energy source for thermophilic autotrophs in marine geothermal environments.

Pyrodictium delaneyi sp. nov., a hyperthermophilic autotrophic archaeon that reduces Fe(III) oxide and nitrate

A hyperthermophilic, autotrophic iron and nitrate reducer, strain Su06T, was isolated from an active deep-sea hydrothermal vent chimney on the Endeavour Segment in the north-eastern Pacific Ocean. It was obligately anaerobic, hydrogenotrophic and reduced Fe(III) oxide to magnetite and NO3- to N2. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the strain was more than 97 % similar to other species of the genera Pyrodictium and Hyperthermus. Therefore, overall genome relatedness index analyses were performed to establish whether strain Su06T represents a novel species. For each analysis, strain Su06T was most similar to Pyrodictium occultum PL-19T. Relative to this strain, the average nucleotide identity score for strain Su06T was 72 %, the genome-to-genome direct comparison score was 13-19 % and the species identification score at the protein level was 89 %. For each analysis, strain Su06T was below the species delineation cutoff. Based on its whole genome sequence and its unique phenotypic characteristics, strain Su06T is suggested to represent a novel species of the genus Pyrodictium, for which the name Pyrodictium delaneyi is proposed. The type strain is Su06T (=DSM 28599T=ATCC BAA-2559T).

Hydrogen and thiosulfate limits for growth of a thermophilic, autotrophic Desulfurobacterium species from a deep-sea hydrothermal vent

Hydrothermal fluids (341°C and 19°C) were collected < 1 m apart from a black smoker chimney and a tubeworm mound on the Boardwalk edifice at the Endeavour Segment in the northeastern Pacific Ocean to study anaerobic microbial growth in hydrothermal mineral deposits. Geochemical modelling of mixed vent fluid and seawater suggests the mixture was anoxic above 55°C and that low H2 concentrations (79 μmol kg(-1) in end-member hydrothermal fluid) limit anaerobic hydrogenotrophic growth above this temperature. A thermophilic, hydrogenotrophic sulfur reducer, Desulfurobacterium strain HR11, was isolated from the 19°C fluid raising questions about its H2 -dependent growth kinetics. Strain HR11 grew at 40-77°C (Topt 72-75°C), pH 5-8.5 (pHopt 6-7) and 1-5% (wt vol(-1) ) NaCl (NaClopt 3-4%). The highest growth rates occurred when S2 O3 (2-) and S° were reduced to H2 S. Modest growth occurred by NO3 (-) reduction. Monod constants for its growth were Ks of 30 μM for H2 and Ks of 20 μM for S2 O3 (2-) with a μmax of 2.0 h(-1) . The minimum H2 and S2 O3 (2-) concentrations for growth were 3 μM and 5 μM respectively. Possible sources of S2 O3 (2-) and S° are from abiotic dissolved sulfide and pyrite oxidation by O2 .

Hydrogen Production and Enzyme Activities in the Hyperthermophile Thermococcus paralvinellae Grown on Maltose, Tryptone, and Agricultural Waste

Thermococcus may be an important alternative source of H2 in the hot subseafloor in otherwise low H2 environments such as some hydrothermal vents and oil reservoirs. It may also be useful in industry for rapid agricultural waste treatment and concomitant H2 production. Thermococcus paralvinellae grown at 82°C without sulfur produced up to 5 mmol of H2 L(-1) at rates of 5-36 fmol H2 cell(-1) h(-1) on 0.5% (wt vol(-1)) maltose, 0.5% (wt vol(-1)) tryptone, and 0.5% maltose + 0.05% tryptone media. Two potentially inhibiting conditions, the presence of 10 mM acetate and low pH (pH 5) in maltose-only medium, did not significantly affect growth or H2 production. Growth rates, H2 production rates, and cell yields based on H2 production were the same as those for Pyrococcus furiosus grown at 95°C on the same media for comparison. Acetate, butyrate, succinate, isovalerate, and formate were also detected as end products. After 100 h, T. paralvinellae produced up to 5 mmol of H2 L(-1) of medium when grown on up to 70% (vol vol(-1)) waste milk from cows undergoing treatment for mastitis with the bacterial antibiotic Ceftiofur and from untreated cows. The amount of H2 produced by T. paralvinellae increased with increasing waste concentrations, but decreased in P. furiosus cultures supplemented with waste milk above 1% concentration. All mesophilic bacteria from the waste milk that grew on Luria Bertani, Sheep's Blood (selective for Staphylococcus, the typical cause of mastitis), and MacConkey (selective for Gram-negative enteric bacteria) agar plates were killed by heat during incubation at 82°C. Ceftiofur, which is heat labile, was below the detection limit following incubation at 82°C. T. paralvinellae also produced up to 6 mmol of H2 L(-1) of medium when grown on 0.1-10% (wt vol(-1)) spent brewery grain while P. furiosus produced < 1 mmol of H2 L(-1). Twelve of 13 enzyme activities in T. paralvinellae showed significant (p < 0.05) differences across six different growth conditions; however, methyl viologen-dependent membrane hydrogenase activity remained constant across all media types. The results demonstrate the potential of at least some Thermococcus species to produce H2 if protein and α-glucosides are present as substrates.

M ethanocaldococcus bathoardescens sp. nov., a hyperthermophilic methanogen isolated from a volcanically active deep-sea hydrothermal vent

A hyperthermophilic methanogen, strain JH146T, was isolated from 26 °C hydrothermal vent fluid emanating from a crack in basaltic rock at Marker 113 vent, Axial Seamount in the northeastern Pacific Ocean. It was identified as an obligate anaerobe that uses only H2 and CO2 for growth. Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain is more than 97 % similar to other species of the genus Methanocaldococcus . Therefore, overall genome relatedness index analyses were performed to establish that strain JH146T represents a novel species. For each analysis, strain JH146T was most similar to Methanocaldococcus sp. FS406-22, which can fix N2 and also comes from Marker 113 vent. However, strain JH146T differs from strain FS406-22 in that it cannot fix N2. The average nucleotide identity score for strain JH146T was 87 %, the genome-to-genome direct comparison score was 33–55 % and the species identification score was 93 %. For each analysis, strain JH146T was below the species delineation cut-off. Full-genome gene synteny analysis showed that strain JH146T and strain FS406-22 have 97 % genome synteny, but strain JH146T was missing the operons necessary for N2 fixation and assimilatory nitrate reduction that are present in strain FS406-22. Based on its whole genome sequence, strain JH146T is suggested to represent a novel species of the genus Methanocaldococcus for which the name Methanocaldococcus bathoardescens is proposed. The type strain is JH146T ( = DSM 27223T = KACC 18232T).

Thermococcus paralvinellae sp. nov. and Thermococcus cleftensis sp. nov. of hyperthermophilic heterotrophs from deep-sea hydrothermal vents

Two heterotrophic hyperthermophilic strains, ES1T and CL1T, were isolated from Paralvinella sp. polychaete worms collected from active hydrothermal vent chimneys in the north-eastern Pacific Ocean. Both were obligately anaerobic and produced H2S in the presence of elemental sulfur and H2. Complete genome sequences are available for both strains. Phylogenetic analyses based on 16S rRNA gene sequences showed that the strains are more than 97 % similar to most other species of the genus Thermococcus . Therefore, overall genome relatedness index analyses were performed to establish that these strains are novel species. For each analysis, strain ES1T was determined to be most similar to Thermococcus barophilus MPT, while strain CL1T was determined to be most similar to Thermococcus sp. 4557. The average nucleotide identity scores for these strains were 84 % for strain ES1T and 81 % for strain CL1T, genome-to-genome direct comparison scores were 23 % for strain ES1T and 47 % for strain CL1T, and the species identification scores were 89 % for strain ES1T and 88 % for strain CL1T. For each analysis, strains ES1T and CL1T were below the species delineation cut-off. Therefore, based on their whole genome sequences, strains ES1T and CL1T are suggested to represent novel species of the genus Thermococcus for which the names Thermococcus paralvinellae sp. nov. and Thermococcus cleftensis sp. nov. are proposed, respectively. The type strains are ES1T ( = DSM 27261T = KACC 17923T) and CL1T ( = DSM 27260T = KACC 17922T).

Structural features underlying the selective cleavage of a novel exo-type maltose-forming amylase fromPyrococcussp. ST04

A novel maltose-forming α-amylase (PSMA) was recently found in the hyperthermophilic archaeonPyrococcussp. ST04. This enzyme shows <13% amino-acid sequence identity to other known α-amylases and displays a unique enzymatic property in that it hydrolyzes both α-1,4-glucosidic and α-1,6-glucosidic linkages of substrates, recognizing only maltose units, in an exo-type manner. Here, the crystal structure of PSMA at a resolution of 1.8 Å is reported, showing a tight ring-shaped tetramer with monomers composed of two domains: an N-domain (amino acids 1–341) with a typical GH57 family (β/α)7-barrel fold and a C-domain (amino acids 342–597) composed of α-helical bundles. A small closed cavity observed in proximity to the catalytic residues Glu153 and Asp253 at the domain interface has the appropriate volume and geometry to bind a maltose unit, accounting for the selective exo-type maltose hydrolysis of the enzyme. A narrow gate at the putative subsite +1 formed by residue Phe218 and Phe452 is essential for specific cleavage of glucosidic bonds. The closed cavity at the active site is connected to a short substrate-binding channel that extends to the central hole of the tetramer, exhibiting a geometry that is significantly different from classical maltogenic amylases or β-amylases. The structural features of this novel exo-type maltose-forming α-amylase provide a molecular basis for its unique enzymatic characteristics and for its potential use in industrial applications and protein engineering.

Magnetite formation from ferrihydrite by hyperthermophilic archaea from Endeavour Segment, Juan de Fuca Ridge hydrothermal vent chimneys

Hyperthermophilic iron reducers are common in hydrothermal chimneys found along the Endeavour Segment in the northeastern Pacific Ocean based on culture-dependent estimates. However, information on the availability of Fe(III) (oxyhydr) oxides within these chimneys, the types of Fe(III) (oxyhydr) oxides utilized by the organisms, rates and environmental constraints of hyperthermophilic iron reduction, and mineral end products is needed to determine their biogeochemical significance and are addressed in this study. Thin-section petrography on the interior of a hydrothermal chimney from the Dante edifice at Endeavour showed a thin coat of Fe(III) (oxyhydr) oxide associated with amorphous silica on the exposed outer surfaces of pyrrhotite, sphalerite, and chalcopyrite in pore spaces, along with anhydrite precipitation in the pores that is indicative of seawater ingress. The iron sulfide minerals were likely oxidized to Fe(III) (oxyhydr) oxide with increasing pH and Eh due to cooling and seawater exposure, providing reactants for bioreduction. Culture-dependent estimates of hyperthermophilic iron reducer abundances in this sample were 1740 and 10 cells per gram (dry weight) of material from the outer surface and the marcasite-sphalerite-rich interior, respectively. Two hyperthermophilic iron reducers, Hyperthermus sp. Ro04 and Pyrodictium sp. Su06, were isolated from other active hydrothermal chimneys on the Endeavour Segment. Strain Ro04 is a neutrophilic (pH opt 7-8) heterotroph, while strain Su06 is a mildly acidophilic (pH opt 5), hydrogenotrophic autotroph, both with optimal growth temperatures of 90-92 °C. Mössbauer spectroscopy of the iron oxides before and after growth demonstrated that both organisms form nanophase (<12 nm) magnetite [Fe3 O4 ] from laboratory-synthesized ferrihydrite [Fe10 O14 (OH)2 ] with no detectable mineral intermediates. They produced up to 40 mm Fe(2+) in a growth-dependent manner, while all abiotic and biotic controls produced <3 mm Fe(2+) . Hyperthermophilic iron reducers may have a growth advantage over other hyperthermophiles in hydrothermal systems that are mildly acidic where mineral weathering at increased temperatures occurs.

Bioinformatic and biochemical analysis of a novel maltose-forming α-amylase of the GH57 family in the hyperthermophilic archaeon Thermococcus sp. CL1

Maltose-forming α-amylase is a glycoside hydrolase family 57 (GH57) member that is unique because it displays dual hydrolysis activity toward α-1,4- and α-1,6-glycosidic linkages and only recognizes maltose. This enzyme was previously identified only in Pyrococcus sp. ST04 (PSMA); however, we recently found two homologs subgroups in Thermococcus species. One subgroup (subgroup A) showed relatively high amino acid sequence similarity to PSMA (>71%), while the other subgroup (subgroup B) showed lower homology with PSMA (<59%). To characterize the subgroup B maltose-forming α-amylase from Thermococcus species (TCMA), we cloned the CL1_0868 gene from Thermococcus sp. CL1 and then successfully expressed the gene in Escherichia coli. Although TCMA has a different oligomeric state relative to PSMA, TCMA showed similar substrate specificity. However, TCMA was shown to hydrolyze maltooligosaccharides more easily than PSMA. Also, TCMA displayed different optimum conditions depending on the glycosidic linkage of the substrate. TCMA had the highest activity at 85°C and at pH 5.0 for α-1,4-glycosidic linkage hydrolysis whereas it showed its maximal activity to cleave α-1,6-glycosidic linkages at 98°C and pH 6.0.

Growth kinetics and energetics of a deep-sea hyperthermophilic methanogen under varying environmental conditions

A hyperthermophilic deep-sea methanogen, Methanocaldococcus strain JH146, was isolated from 26°C hydrothermal fluid at Axial Volcano to model high temperature methanogenesis in the subseafloor. Emphasis was placed on defining growth kinetics, cell yields and growth energy demand (GE) across a range of conditions. The organism uses H2 and CO2 as its sole carbon and energy sources. At various temperatures, pHs, and chlorinities, its growth rates and cell yields co-varied while GE remained uniform at 1.69 × 10(-11) J cell(-1)s(-1) ± 0.68 × 10(-11) J cell(-1)s(-1) (s.d., n = 23). An exception was at superoptimal growth temperatures where GE increased to 7.25 × 10(-11) J cell(-1)s(-1) presumably due to heat shock. GE also increased from 5.1 × 10(-12) J cell(-1)s(-1) to 7.61 × 10(-11) J cell(-1)s(-1) as NH4 (+) concentrations decreased from 9.4 mM to 0.14 mM. JH146 did not fix N2 or assimilate NO3 (-), lacked the N2-fixing (cluster II) nifH gene, and became nitrogen limited below 0.14 mM NH4Cl. Nitrogen availability may impact growth in situ since ammonia concentrations at Axial Volcano are < 18 μM. Our approach contributes to refining bioenergetic and carbon flux models for methanogens and other organisms in hydrothermal vents and other environments.

Identification of membrane proteins in the hyperthermophilic archaeon pyrococcus furiosus using proteomics and prediction programs

Cell-free extracts from the hyperthermophilic archaeon Pyrococcus furiosus were separated into membrane and cytoplasmic fractions and each was analyzed by 2D-gel electrophoresis. A total of 66 proteins were identified, 32 in the membrane fraction and 34 in the cytoplasmic fraction. Six prediction programs were used to predict the subcellular locations of these proteins. Three were based on signal-peptides (SignalP, TargetP, and SOSUISignal) and three on transmembrane-spanning α-helices (TSEG, SOSUI, and PRED-TMR2). A consensus of the six programs predicted that 23 of the 32 proteins (72%) from the membrane fraction should be in the membrane and that all of the proteins from the cytoplasmic fraction should be in the cytoplasm. Two membrane-associated proteins predicted to be cytoplasmic by the programs are also predicted to consist primarily of transmembrane-spanning β-sheets using porin protein models, suggesting that they are, in fact, membrane components. An ATPase subunit homolog found in the membrane fraction, although predicted to be cytoplasmic, is most likely complexed with other ATPase subunits in the membrane fraction. An additional three proteins predicted to be cytoplasmic but found in the membrane fraction, may be cytoplasmic contaminants. These include a chaperone homolog that may have attached to denatured membrane proteins during cell fractionation. Omitting these three proteins would boost the membrane-protein predictability of the models to near 80%. A consensus prediction using all six programs for all 2242 ORFs in the P. furiosus genome estimates that 24% of the ORF products are found in the membrane. However, this is likely to be a minimum value due to the programs’ inability to recognize certain membrane-related proteins, such as subunits associated with membrane complexes and porin-type proteins.

Abundances of hyperthermophilic autotrophic Fe(III) oxide reducers and heterotrophs in hydrothermal sulfide chimneys of the northeastern Pacific Ocean

The abundances of hyperthermophilic heterotrophs, methanogens, and autotrophic reducers of amorphous Fe(III) oxide in 18 samples of deep-sea hydrothermal vent sulfide chimneys of the Endeavour Segment were measured. The results indicate that conditions favor the growth of iron reducers toward the interiors of these deposits and that of heterotrophs toward the outer surfaces near high-temperature polychaete worms (Paralvinella sulfincola).

Constraints on anaerobic respiration in the hyperthermophilic Archaea Pyrobaculum islandicum and Pyrobaculum aerophilum

Pyrobaculum islandicum uses iron, thiosulfate, and elemental sulfur for anaerobic respiration, while Pyrobaculum aerophilum uses iron and nitrate; however, the constraints on these processes and their physiological mechanisms for iron and sulfur reduction are not well understood. Growth rates on sulfur compounds are highest at pH 5 to 6 and highly reduced (<-420-mV) conditions, while growth rates on nitrate and iron are highest at pH 7 to 9 and more-oxidized (>-210-mV) conditions. Growth on iron expands the known pH range of growth for both organisms. P. islandicum differs from P. aerophilum in that it requires direct contact with insoluble iron oxide for growth, it did not produce any extracellular compounds when grown on insoluble iron, and it lacked 2,6-anthrahydroquinone disulfonate oxidase activity. Furthermore, iron reduction in P. islandicum appears to be completely independent of c-type cytochromes. Like that in P. aerophilum, NADH-dependent ferric reductase activity in P. islandicum increased significantly in iron-grown cultures relative to that in non-iron-grown cultures. Proteomic analyses showed that there were significant increases in the amounts of a putative membrane-bound thiosulfate reductase in P. islandicum cultures grown on thiosulfate relative to those in cultures grown on iron and elemental sulfur. This is the first evidence of this enzyme being used in either a hyperthermophile or an archaeon. Pyrobaculum arsenaticum and Pyrobaculum calidifontis also grew on Fe(III) citrate and insoluble iron oxide, but only P. arsenaticum could grow on insoluble iron without direct contact.

Characterization of malate dehydrogenase from the hyperthermophilic archaeon Pyrobaculum islandicum

Native and recombinant malate dehydrogenase (MDH) was characterized from the hyperthermophilic, facultatively autotrophic archaeon Pyrobaculum islandicum. The enzyme is a homotetramer with a subunit mass of 33 kDa. The activity kinetics of the native and recombinant proteins are the same. The apparent K ( m ) values of the recombinant protein for oxaloacetate (OAA) and NADH (at 80 degrees C and pH 8.0) were 15 and 86 microM, respectively, with specific activity as high as 470 U mg(-1). Activity decreased more than 90% when NADPH was used. The catalytic efficiency of OAA reduction by P. islandicum MDH using NADH was significantly higher than that reported for any other archaeal MDH. Unlike other archaeal MDHs, specific activity of the P. islandicum MDH back-reaction also decreased more than 90% when malate and NAD(+) were used as substrates and was not detected with NADP(+). A phylogenetic tree of 31 archaeal MDHs shows that they fall into 5 distinct groups separated largely along taxonomic lines suggesting minimal lateral mdh transfer between Archaea.

Citric acid cycle in the hyperthermophilic archaeon Pyrobaculum islandicum grown autotrophically, heterotrophically, and mixotrophically with acetate

The hyperthermophilic archaeon Pyrobaculum islandicum uses the citric acid cycle in the oxidative and reductive directions for heterotrophic and autotrophic growth, respectively, but the control of carbon flow is poorly understood. P. islandicum was grown at 95 degrees C autotrophically, heterotrophically, and mixotrophically with acetate, H2, and small amounts of yeast extract and with thiosulfate as the terminal electron acceptor. The autotrophic growth rates and maximum concentrations of cells were significantly lower than those in other media. The growth rates on H2 and 0.001% yeast extract with and without 0.05% acetate were the same, but the maximum concentration of cells was fourfold higher with acetate. There was no growth with acetate if 0.001% yeast extract was not present, and addition of H2 to acetate-containing medium greatly increased the growth rates and maximum concentrations of cells. P. islandicum cultures assimilated 14C-labeled acetate in the presence of H2 and yeast extract with an efficiency of 55%. The activities of 11 of 19 enzymes involved in the central metabolism of P. islandicum were regulated under the three different growth conditions. Pyruvate synthase and acetate:coenzyme A (CoA) ligase (ADP-forming) activities were detected only in heterotrophically grown cultures. Citrate synthase activity decreased in autotrophic and acetate-containing cultures compared to the activity in heterotrophic cultures. Acetylated citrate lyase, acetate:CoA ligase (AMP forming), and phosphoenolpyruvate carboxylase activities increased in autotrophic and acetate-containing cultures. Citrate lyase activity was higher than ATP citrate synthase activity in autotrophic cultures. These data suggest that citrate lyase and AMP-forming acetate:CoA ligase, but not ATP citrate synthase, work opposite citrate synthase to control the direction of carbon flow in the citric acid cycle.

Characterization of dissimilatory Fe(III) versus NO3- reduction in the hyperthermophilic archaeon Pyrobaculum aerophilum

The hyperthermophilic archaeon Pyrobaculum aerophilum used 20 mM Fe(III) citrate, 100 mM poorly crystalline Fe(III) oxide, and 10 mM KNO3 as terminal electron acceptors. The two forms of iron were reduced at different rates but with equal growth yields. The insoluble iron was reduced when segregated spatially by dialysis tubing, indicating that direct contact with the iron was not necessary for growth. When partitioned, there was no detectable Fe(III) or Fe(II) outside of the tubing after growth, suggesting that an electron shuttle, not a chelator, may be used as an extracellular mediator of iron reduction. The addition of 25 and 50% (vol vol(-1)) cell-free spent insoluble iron media to fresh media led to growth without a lag phase. Liquid chromatography analysis of spent media showed that cultures grown in iron, especially insoluble iron, produced soluble extracellular compounds that were absent or less abundant in spent nitrate medium. NADH-dependent ferric reductase activity increased approximately 100-fold, while nitrate reductase activity decreased 10-fold in whole-cell extracts from iron-grown cells relative to those from nitrate-grown cells, suggesting that dissimilatory iron reduction was regulated. A novel 2,6-anthrahydroquinone disulfonate oxidase activity was more than 580-fold higher in iron-grown cells than in nitrate-grown cells. The activity was primarily (>95%) associated with the membrane cellular fraction, but its physiological function is unknown. Nitrate-grown cultures produced two membrane-bound, c-type cytochromes that are predicted to be monoheme and part of nitrite reductase and a bc1 complex using genome analyses. Only one cytochrome was present in cells grown on Fe(III) citrate whose relative abundance was unchanged.

Identification of 2D-gel proteins: a comparison of MALDI/TOF peptide mass mapping to mu LC-ESI tandem mass spectrometry

A comparative analysis of protein identification for a total of 162 protein spots separated by two-dimensional gel electrophoresis from two fully sequenced archaea, Methanococcus jannaschii and Pyrococcus furiosus, using MALDI-TOF peptide mass mapping (PMM) and mu LC-MS/MS is presented. 100% of the gel spots analyzed were successfully matched to the predicted proteins in the two corresponding open reading frame databases by mu LC-MS/MS while 97% of them were identified by MALDI-TOF PMM. The high success rate from the PMM resulted from sample desalting/concentrating with ZipTip(C18) and optimization of several PMM search parameters including a 25 ppm average mass tolerance and the application of two different protein molecular weight search windows. By using this strategy, low-molecular weight (<23 kDa) proteins could be identified unambiguously with less than 5 peptide matches. Nine percent of spots were identified as containing multiple proteins. By using mu LC-MS/MS, 50% of the spots analyzed were identified as containing multiple proteins. mu LC-MS/MS demonstrated better protein sequence coverage than MALDI-TOF PMM over the entire mass range of proteins identified. MALDI-TOF and PMM produced unique peptide molecular weight matches that were not identified by mu LC-MS/MS. By incorporating amino acid sequence modifications into database searches, combined sequence coverage obtained from these two complimentary ionization methods exceeded 50% for approximately 70% of the 162 spots analyzed. This improved sequence coverage in combination with enzymatic digestions of different specificity is proposed as a method for analysis of post-translational modification from 2D-gel separated proteins.

Microbe-metal interactions in marine hydrothermal environments

Marine hydrothermal microorganisms respond rapidly to changes in the concentrations and availability of metals within their environment. Hyperthermophilic archaea appear to possess novel mechanisms for metal detoxification, dissimilatory metal reduction and metal assimilation that may be absent in their mesophilic and bacterial counterparts. For example, tungsten was found in high concentrations in a hydrothermal sulfide deposit where hyperthermophiles were also most abundant, consistent with the unique requirement of these organisms for this element. Furthermore, newly isolated genera of iron-reducing hyperthermophiles expand the scope of carbon cycling in hydrothermal environments. The advent of genome sequences and new molecular techniques will facilitate our further understanding of microbe-mineral interactions in these environments.

Determination of polydextrose in foods by ion chromatography: collaborative study

Eight collaborating laboratories assayed 7 blind duplicate pairs of foods for polydextrose content. The 7 test sample pairs ranged from low (2%) to high (95%) levels. The following foods were prepared with polydextrose mixed into the other ingredients and then baked, cooked, or otherwise prepared: milk chocolate candy, iced tea, sugar cookie, grape jelly, soft jellied candy, and powdered drink mix. Collaborators received a polydextrose standard to develop a calibration curve. The method determined polydextrose by ion chromatography, after removal of interfering food components (high molecular weight solubles). Repeatability standard deviations (RSDr) ranged from 3.93 to 9.04%; reproducibility standard deviations (RSDR) ranged from 4.48 to 14.06%. The average recovery was 94%.

Phosphoenolpyruvate synthetase from the hyperthermophilic archaeon Pyrococcus furiosus

Phosphoenolpyruvate synthetase (PpsA) was purified from the hyperthermophilic archaeon Pyrococcus furiosus. This enzyme catalyzes the conversion of pyruvate and ATP to phosphoenolpyruvate (PEP), AMP, and phosphate and is thought to function in gluconeogenesis. PpsA has a subunit molecular mass of 92 kDa and contains one calcium and one phosphorus atom per subunit. The active form has a molecular mass of 690+/-20 kDa and is assumed to be octomeric, while approximately 30% of the protein is purified as a large ( approximately 1.6 MDa) complex that is not active. The apparent K(m) values and catalytic efficiencies for the substrates pyruvate and ATP (at 80 degrees C, pH 8.4) were 0.11 mM and 1.43 x 10(4) mM(-1). s(-1) and 0.39 mM and 3.40 x 10(3) mM(-1) x s(-1), respectively. Maximal activity was measured at pH 9.0 (at 80 degrees C) and at 90 degrees C (at pH 8.4). The enzyme also catalyzed the reverse reaction, but the catalytic efficiency with PEP was very low [k(cat)/K(m) = 32 (mM. s(-1)]. In contrast to several other nucleotide-dependent enzymes from P. furiosus, PpsA has an absolute specificity for ATP as the phosphate-donating substrate. This is the first PpsA from a nonmethanogenic archaeon to be biochemically characterized. Its kinetic properties are consistent with a role in gluconeogenesis, although its relatively high cellular concentration ( approximately 5% of the cytoplasmic protein) suggests an additional function possibly related to energy spilling. It is not known whether interconversion between the smaller, active and larger, inactive forms of the enzyme has any functional role.

Key role for sulfur in peptide metabolism and in regulation of three hydrogenases in the hyperthermophilic archaeon Pyrococcus furiosus

The hyperthermophilic archaeon Pyrococcus furiosus grows optimally at 100 degrees C by the fermentation of peptides and carbohydrates. Growth of the organism was examined in media containing either maltose, peptides (hydrolyzed casein), or both as the carbon source(s), each with and without elemental sulfur (S(0)). Growth rates were highest on media containing peptides and S(0), with or without maltose. Growth did not occur on the peptide medium without S(0). S(0) had no effect on growth rates in the maltose medium in the absence of peptides. Phenylacetate production rates (from phenylalanine fermentation) from cells grown in the peptide medium containing S(0) with or without maltose were the same, suggesting that S(0) is required for peptide utilization. The activities of 14 of 21 enzymes involved in or related to the fermentation pathways of P. furiosus were shown to be regulated under the five different growth conditions studied. The presence of S(0) in the growth media resulted in decreases in specific activities of two cytoplasmic hydrogenases (I and II) and of a membrane-bound hydrogenase, each by an order of magnitude. The primary S(0)-reducing enzyme in this organism and the mechanism of the S(0) dependence of peptide metabolism are not known. This study provides the first evidence for a highly regulated fermentation-based metabolism in P. furiosus and a significant regulatory role for elemental sulfur or its metabolites.

Determination of polydextrose as dietary fiber in foods

Polydextrose (Litesse) provides physiological effects consistent with dietary fiber. However, AOAC methods for measuring total dietary fiber (TDF) in foods include an ethanol precipitation step in which polydextrose and similar carbohydrates are discarded and therefore not quantitated. This study describes a method developed to quantitate polydextrose in foods. The new method includes water extraction, centrifugal ultrafiltration, multienzyme hydrolysis, and anion exchange chromatography with electrochemical detection. Six foods were prepared with 4 levels of polydextrose to test the ruggedness of the method. Internal validation demonstrated the ruggedness of the method with recoveries ranging from 83 to 104% with an average of 95% (n = 24) and relative standard deviation of recoveries ranging from 0.7 to 13% with an average of 3.3% (n = 24). The value is added to that obtained for dietary fiber content of foods using the AOAC methods, to determine the TDF content of the food.

Enhanced thermotolerance and temperature-induced changes in protein composition in the hyperthermophilic archaeon ES4

The hyperthermophilic archaeon ES4, a heterotrophic sulfur reducer isolated from a deep-sea hydrothermal vent, is capable of protecting itself from thermal stress at temperatures above its optimum for growth. The thermotolerance of ES4 was determined by exposing log-phase cells to various lethal high temperatures. When ES4 was shifted from 95 to 102 degrees C, it displayed recovery from an exponential rate of death, followed by transient thermotolerance. When ES4 was shifted directly from 95 to either 105 or 108 degrees C, only exponential death occurred. However, a shift from 95 to 105 degrees C with an intermediate incubation at 102 degrees C also gave ES4 transient thermotolerance to 105 degrees C. The protein composition of ES4 was examined at temperatures ranging from 75 to 102 degrees C by one-dimensional electrophoresis. Two proteins with molecular masses of approximately 90 and 150 kDa significantly decreased in abundance with increasing growth temperature, while a 98-kDa protein, present at very low levels at normal growth temperatures (76 to 99 degrees C), was more abundant at higher temperatures. The enhanced tolerance to hyperthermal conditions after a mild hyperthermal exposure and the increased abundance of the 98-kDa protein at above-optimal temperatures imply that ES4 is capable of a heat shock-like response previously unseen in hyperthermophilic archaea.